The present invention relates to a rotary armature of an electric motor and a method for forming an armature coil and, more particularly to a rotary armature on which a multi-coil structure form is performed and a method for forming an armature coil suitable for use in an electric starter motor for an automobile.
As a coil which is wound with a multi-coil structure form on a slot of a rotary armature of an electric motor, a coil having a circular-shaped cross-sectional form is disclosed, for example, in Japanese patent laid-open No. 121,452/1988, Japanese patent laid-open No. 265,534/1988 and Japanese patent laid-open No. 305,737/1988, further a coil having a flat quadrilateral-shaped cross-sectional form has been known, and also an insulated coating wire having a flat quadrilateral-shaped cross-sectional form by forming an insulated coating wire having a circular-shaped cross-sectional form through a pressing process under pressure is disclosed, for example, in Japanese patent laid-open No. 240,832/1986.
In the above stated prior arts, so as to improve the space factor during the coil is wound with the multi-coil structure form in the slot, a central conductor portion (a slot insertion conductor portion) is performed from the insulated coating wire having the circular-shaped cross-sectional form to the insulated coating wire having the flat quadrilateral-shaped cross-sectional form. Accordingly, it contrives to lessen a dead space at the inner peripheral wall surface of the slot or the conductor.
However, there takes no consideration about a problem the space factor is suffered to lessen enough the thickness of the insulated coating film of the coil.
Namely, after by forming the central conductor portion with a predetermined cross-sectional form, in a case the central conductor portion is coated according to the insulated coating film, since the thickness of the insulated coating film is formed uniformly at a whole periphery, however it is impossible to lessen the dead space at the inner peripheral wall surface of the slot or the conductor.
Further, in a case that the coil has the flat quadrilateral-shaped cross-sectional form, in particularly, in a case the armature core in which the insulated coating wire is inserted into the slot from an axial direction, so as not to peel an insulated coating member at an inlet portion or a midway portion of the slot it is necessary to insulate the magnetic core in accordance the employment of an insulating sheet (thickness of the insulating sheet 0.3-0.5 mm degree, in ordinary).
Accordingly, even in a case that the insulating sheet is inserted, it is unavoidable to lessen the space factor enough the thickness of a pair of insulated coating films having the flat quadrilateral-shaped cross-sectional form being opposite each other.
Besides, in a case that the coil in which the central conductor portion having the circular-shaped cross-sectional form is coated by the insulated coating film and this coil is formed to have the flat quadrilateral-shaped cross-sectional form according to the pressing process under pressure merely from an upper direction and a lower direction.
In the processed coil formed on the imaginary at the flat quadrilateral-shaped cross-sectional form, however the central conductor portion is formed substantially with a multangular-shaped form. Accordingly, the thickness of the insulated coating film does not change hardly, in this case the space factor of the slot does not increase.
This space factor of the slot gives a large affect on the electric motor in which a small size and a high output of the electric motor are required, as a result it is advisable to improve the space factor of the slot.